1. H. Poincaré,Arch. Neerl. 5, 252 (1900).
2. H. Poincaré,Bull. Sci. Math. 28, 306 (1904) [transl.:Bull. Am. Math. Soc. 12, 240 (1906)]; see alsoThe Foundations of Science (transl. by G. B. Halsted, The Science Press, New York, 1921), pp. 303?313.
3. A. Einstein,Ann. Phys. 17, 891 (1905); see alsoRelativity, The Special and the General Theory (transl. by R. W. Lawson, Crown Publishers, New York, 1961), pp. 21?27.
4. R. P. Feynman,The Character of Physical Law (MIT Press, Cambridge, Mass., 1965), pp. 91?92.
5. H. Poincaré,Revue de Métaphysique et de Morale, VI, 1 (January 1898).